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Journal of Clinical Microbiology, July 2003, p. 3413-3414, Vol. 41, No. 7
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.7.3413-3414.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Molecular Analysis of Clostridium difficile Strains Isolated from 18 Cases of Recurrent Clostridium difficile-Associated Diarrhea
Yajarayma Tang-Feldman, Susan Mayo, Joseph Silva, Jr., and Stuart H. Cohen*
Department of Internal Medicine, Division of Infectious and Immunologic Diseases, University of California, Davis Medical Center, Sacramento, California 95817
Received 2 December 2002/
Returned for modification 21 January 2003/
Accepted 30 March 2003

ABSTRACT
Recurrence of
Clostridium difficile-associated diarrhea (CDAD)
occurs in 15 to 20% of patients after discontinuation of treatment.
Arbitrarily primed PCR was used to investigate the epidemiology
of recurrent CDAD in 18 patients. Reinfection with a new strain
occurred in 6 of 18 patients (33.3%), while 12 patients relapsed
with the original strain shortly after discontinuation of treatment.
These data suggest that reinfection with exogenous
C. difficile is a common problem and that not all recurrences are due to
relapse.

TEXT
Clostridium difficile-associated diarrhea (CDAD) is the most
common hospital-acquired infectious diarrhea. Treatment of CDAD
is primarily with metronidazole or vancomycin; however, between
15 and 20% of patients have recurrences following discontinuation
of therapy (
10). It is believed that these are relapses due
to persistence of spores in the gut after treatment (
2). The
possibility of recurrent disease due to environmental contamination
and reinfection was considered early in 1980 (
11). Only a limited
number of studies have been performed that investigate the rate
of reinfection in
C. difficile infections. In a study reported
by Johnson et al., 45% (5 of 11) of patients were reinfected
with a new strain (
7). O'Neill et al. found a 75% reinfection
rate among eight inpatients and two outpatients analyzed by
restriction endonuclease analysis (
8). The goal of this study
was to further investigate the epidemiology of recurrences of
C. difficile infection by determining the rates of true relapses
versus reinfections.
A total of 18 patients with a history of CDAD recurrences were analyzed in this study. All patients were diagnosed as having CDAD by the cytotoxicity assay. Multiple isolates (at least two) were obtained from each patient. Twelve of these patients were inpatients at the University of California, Davis Medical Center. Three were outpatients at University of California, Davis Medical Center, and three were outpatients at the University of Michigan Medical Center, Ann Arbor.
Stock cultures from patients were inoculated on cycloserine-cefoxitin-fructose agar plates (6) and were grown anaerobically at 37°C for 48 h. DNA was extracted from a single colony from each plate as described elsewhere (9). Arbitrarily primed PCR that relies on the T7 oligonucleotide was used to identify different strains (9). This method has been used before and has been validated to other typing methods (3, 4, 9). Amplification products were run by electrophoresis on 1.5% agarose gels (Gibco BRL, Grand Island, N.Y.). Gels were stained with ethidium bromide (0.5 µg/ml), destained, and analyzed visually by using the Quantity One software package with the Molecular Analyst Fingerprinting software (Bio-Rad, Hercules, Calif.).
Six of the eighteen recurrences (33.3%) were due to reinfection with exogenous C. difficile strains, while 12 of 18 (66.7%) were true relapses. In the inpatient population, 4 of 12 (33.3%) CDAD cases were due to reinfection and 8 of 12 (66.6%) were relapses. In the outpatient population, 33.3% (two of six) of patients were found to have reinfection and 66% (four of six) relapsed approximately 1 to 7 months afterward (Table 1). Figure 1 shows the DNA-banding patterns of selected isolates representing reinfection or true relapses.
Reinfection with
C. difficile occurred both in inpatient and
outpatient settings. True relapses were common in inpatients
whose recurrent CDAD was diagnosed shortly after discontinuation
of treatment. This observation suggests the persistence of spores
in the gastrointestinal tract of these patients. One outpatient
from whom four isolates were obtained was reinfected with multiple
strains during a 7-month period. It is possible that these outpatients
are colonized by multiple isolates even when they are asymptomatic
or that they acquire new strains from environmental sources.
Our results are in agreement with those of others who have investigated
the nature of relapses. The rate of recurrences varies in reports
from 5 to 66%, with a rate of 20% considered average (
5,
7).
Johnson et al. and O'Neill et al. found that 45 to 60% of recurrences
were due to reinfection with new strains (
7,
8). Most of these
studies have been done on inpatients. A study of CDAD recurrences
in human immunodeficiency virus-infected patients found that
64% of the recurrences were due to relapses, while 32% were
reinfections and 4% were a combination of relapse and reinfection
(
1). In a number of studies, an association has been established
between the persistence of the organism and relapses. The finding
that 66.6% of inpatients had a true relapse shortly after discontinuation
of treatment may be explained as incomplete eradication of the
organism and its persistence in spore form.
In summary, our results show that reinfection with exogenous C. difficile is a common problem and that not all recurrent CDAD is due to true relapses.

ACKNOWLEDGMENTS
We thank F. Robert Fekety for providing some of the isolates
used in this study (F. Robert Fekety,
C. difficile Culture Collection,
Ann Arbor, Michigan).

FOOTNOTES
* Corresponding author. Mailing address: Division of Infectious and Immunologic Diseases, Dept. of Internal Medicine, Patient Services and Support Building, 4150 V St., Suite 500, Sacramento, CA 95817. Phone: (916) 734-3741. Fax: (916) 734-7766. E-mail:
stcohen{at}ucdavis.edu.


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Journal of Clinical Microbiology, July 2003, p. 3413-3414, Vol. 41, No. 7
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.7.3413-3414.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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